JP2020184472A - Positive electrode for non-aqueous electrolyte power storage element, and non-aqueous electrolyte power storage element including the same - Google Patents

Abstract

To provide a positive electrode for a non-aqueous electrolyte power storage element having a high electrode density without impairing a high discharge capacity.SOLUTION: A positive electrode for a non-aqueous electrolyte power storage element includes a lithium excess type positive electrode active material, an amorphous carbon, and graphite.SELECTED DRAWING: Figure 6

Description

The present invention relates to a positive electrode for a non-aqueous electrolyte power storage element and a non-aqueous electrolyte power storage element provided with the positive electrode.

Non-aqueous electrolyte storage elements represented by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. due to their high energy density. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte storage elements other than lithium ion secondary batteries.

Active materials such as LiCoO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Co _0,2 Mn _0.3 O ₂ are known as positive electrode active materials for non-aqueous electrolyte power storage elements. ing. These so-called "LiMeO type ₂ " active materials have an α-NaFeO type ₂ crystal structure, and the molar ratio of Li to the transition metal (Me) (Li / Me) is less than 1.1, typically. It is around 1.

On the other hand, as a positive electrode active material for a non-aqueous electrolyte power storage element capable of obtaining a high discharge capacity, the composition ratio Li / Me of lithium (Li) to the transition metal (Me) is larger than 1, for example, Li / Me is 1.1 to 1. A lithium-rich active material, which is 0.6, is known. The lithium excess type active material can be expressed as the composition formula Li _{1 + α} Me _1-α O ₂ (α> 0). Here, assuming that the composition ratio Li / Me of lithium (Li) to the ratio of the transition metal (Me) is β, β = (1 + α) / (1-α), so for example, Li / Me is 1.5. When, α = 0.2.

The non-aqueous electrolyte power storage element is required to be further miniaturized from the viewpoint of loading space and portability. One means of solving this problem is to improve the mixture density of electrodes (hereinafter referred to as "electrode density").

Patent Document 1 states, "By setting the average thickness of flaky graphite to 0.5 μm or less, the deformability of flaky graphite becomes good, and the flaky graphite can be deformed according to the shape of the positive electrode active material. It is possible to improve the density of the active material layer. ”(Paragraph 0019). Then, the so-called "LiMeO type ₂ " active material, lithium nickel composite oxide LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , was used as the positive electrode active material, and "the density of the positive electrode active material layer at the same linear pressure". A positive electrode having a value of 3.60 g / cm ³ is described (Example 1, Table 1). However, Patent Document 1 does not describe the improvement of the electrode density when the lithium excess type positive electrode active material is used.

In Tables 2 and 3 of Patent Document 2, a lithium excess type positive electrode active material having a Ni / Co / Mn ratio of 30/15/55 and a Li / Me ratio of 1.2 is used, and "mixture density" is used. There cathode is described which is 2.56 g / cm ³ to 3.05 g / cm ^3. Further, Table 4, using a lithium-excess type positive electrode active material of various compositions, "mixture density" is the positive electrode is described which is 2.64 g / cm ³ to 3.07 g / cm ^3.

WO2017 / 149927 JP-A-2018-073752

An object of the present invention is to provide a positive electrode having a high electrode density, which contains a lithium excess type positive electrode active material and does not impair a high discharge capacity.

One aspect of the present invention is a positive electrode for a non-aqueous electrolyte power storage element containing a lithium excess type positive electrode active material, amorphous carbon, and graphite.

According to the present invention, it is possible to provide a positive electrode containing a lithium excess type positive electrode active material and having a high electrode density without impairing a high discharge capacity, and a non-aqueous electrolyte storage element using the same.

It is an external perspective view which shows one Embodiment of the non-aqueous electrolyte power storage element. It is a schematic diagram which shows one Embodiment of the power storage device which was configured by gathering a plurality of non-aqueous electrolyte power storage elements. It is a figure for demonstrating the mechanism of action of the presumed example. It is an SEM image of the graphite powder used in an Example. FIG. 5 is an X-ray diffraction pattern of a positive electrode after pressing according to Example 1-1 and Comparative Example 1-1. It is a figure which shows the correlation of the peak differential pore volume of a positive electrode active material, and the electrode density of a positive electrode. It is a figure which shows the correlation between the graphite content of a positive electrode and an electrode density, and the graphite content of a positive electrode, and the 2C discharge capacity of a non-aqueous electrolyte power storage element.

The uniform state of the present invention is a positive electrode for a non-aqueous electrolyte power storage element containing a lithium excess type positive electrode active material, amorphous carbon, and graphite.

Here, the lithium excess type positive electrode active material may have a peak differential pore volume of 0.5 mm ³ / (g · nm) or more.

Another uniform of the present invention is a non-aqueous electrolyte storage element using the positive electrode for the non-aqueous electrolyte storage element.

The configuration and action / effect of the present invention will be described with technical ideas. However, the mechanism of action includes estimation, and its correctness does not limit the present invention. It should be noted that the present invention can be practiced in various other forms without departing from its essence or main features. Therefore, the embodiments or examples described below are merely examples in all respects and should not be construed in a limited manner. Furthermore, all modifications and modifications that fall within the equivalent scope of the claims are within the scope of the present invention.

The positive electrode of the non-aqueous electrolyte power storage element is completed through a pressing process after applying a positive electrode paste containing a positive electrode active material to a positive electrode base material and drying to form a positive electrode mixture layer. By increasing the press pressure in the press process, the electrode density can be increased.

As shown in the reference example described later, it has an α-NaFeO type ₂ crystal structure, and the molar ratio (Li / Me) of Li to the transition metal (Me) is less than 1.1, so-called “LiMeO type ₂ ” activity. When a substance is used for the positive electrode, it is easy to obtain a positive electrode mixture layer having a high electrode density of about 3.3 g / cm ³ . However, although it depends on the thickness of the positive electrode mixture layer and the composition of the positive electrode mixture layer, for example, the content of the positive electrode active material in the positive electrode mixture is 90% by mass or more, and the electrode density is 3.3 g /. In a positive electrode having a size of more than cm ³ , the void ratio of the positive electrode mixture layer is lowered, and the permeability of the electrolytic solution is lowered, so that the electrochemical characteristics such as charge / discharge cycle performance are lowered. Therefore, in the positive electrode using the so-called "LiMeO type ₂ " active material, it is not necessary to increase the electrode density any more.

On the other hand, as can be seen from Patent Documents 1 and 2, the electrode density of the positive electrode using the lithium excess type positive electrode active material is lower than that of the positive electrode using the so-called "LiMeO type ₂ " active material.

As a result of diligent studies on the above problems, the present inventor has made an electrode by using amorphous carbon and graphite as materials constituting the positive electrode mixture in a positive electrode using a lithium excess type positive electrode active material. We have found that the density can be improved.

The mechanism of action that exerts the effect of the present invention is presumed as follows. As shown in Table 1 described later, the lithium excess type positive electrode active material has a larger peak differential pore volume than the so-called “LiMeO type ₂ ” active material. In addition, the total pore volume (cm ³ / g) is large, and the pore diameter (nm) at which the differential pore volume shows the maximum value is also large. From this, it is considered that the lithium excess type positive electrode active material is composed of particles having a large number of pores having a large pore diameter as compared with the so-called “LiMeO type ₂ ” active material. Therefore, in the pressing step after applying the positive electrode paste containing the positive electrode active material to the positive electrode base material and drying to form the positive electrode mixture layer, the positive electrode active material particles constituting the positive electrode mixture layer and other constituent materials are combined. It is considered that a large frictional resistance is generated between them, which is considered to be the reason why a positive electrode having a high electrode density cannot be obtained.

The mechanism of action in which the electrode density is improved by the configuration of the present invention will be described with reference to FIG. Graphite has a structure in which graphene is regularly laminated. Therefore, as shown in FIG. 3 (A), when pressure is applied from the vertical direction of the figure, as shown in FIG. 3 (B), a shift occurs between the layers of graphene, resulting in friction between graphite and other constituent materials. It is considered that the resistance is reduced, and as a result, the electrode density can be improved as compared with the system in which the positive electrode does not contain graphite.

A method of adding carbon nanotubes to the positive electrode is also known in order to improve the electrode density, but carbon nanotubes have poor dispersibility and are very difficult to handle. It is also expensive.

The positive electrode for a non-aqueous electrolyte power storage element according to an embodiment of the present invention will be described in detail below.

(Lithium excess positive electrode active material)
The lithium-rich positive electrode active material according to the present embodiment is typically represented by the composition formula Li _{1 + α} Me _1-α O ₂ (Me: Ni and Mn, or a transition metal containing Ni, Co and Mn). Will be done. In order to obtain a non-aqueous electrolyte storage device having a large discharge capacity, the molar ratio of Li to the transition metal (Me) Li / Me, that is, (1 + α) / (1-α) is preferably larger than 1.1. It is more preferably 2 or more, and particularly preferably 1.3 or more. Further, it is preferably 1.5 or less, more preferably 1.45 or less, and particularly preferably 1.4 or less.

Since Ni has an effect of improving the discharge capacity of the active material, the molar ratio of Ni to the transition metal (Me), Ni / Me, is preferably 0.15 or more, more preferably 0.25 or more, and 0.3 or more. Is particularly preferable. The molar ratio Ni / Me is preferably less than 0.5, more preferably 0.45 or less, and particularly preferably 0.4 or less.
Since Mn has an effect of improving charge / discharge cycle performance from the viewpoint of material cost, the molar ratio of Mn to the transition metal (Me) Mn / Me is preferably larger than 0.5, preferably 0.6. The above is more preferable, and 0.65 or more is particularly preferable. Further, 0.8 or less is preferable, 0.75 or less is more preferable, and 0.7 or less is particularly preferable.
Co has the effect of increasing the electron conductivity of the active material particles and improving the high rate discharge performance, but is an optional element in which a small amount is preferable in terms of charge / discharge cycle performance and economy. The molar ratio of Co to the transition metal (Me), Co / Me, is preferably 0.20 or less, more preferably 0.15 or less, even more preferably 0.05 or less, and may be 0. If a raw material containing Ni is used, Co may be contained as an impurity.

The peak differential pore volume of the lithium excess type positive electrode active material is preferably 0.5 mm ³ / (g · nm) or more, and more preferably 0.6 mm ³ / (g · nm) or more in order to improve the discharge capacity. , 0.7 mm ³ / (g · nm) or more is even more preferable. Further, from the viewpoint of charge / discharge cycle performance, 2.6 mm ³ / (g · nm) or less is preferable, 2.0 mm ³ / (g · nm) or less is more preferable, and 1.5 mm ³ / (g · nm) or less. Is even more preferable.
That is, the peak differential pore volume of the lithium excess type positive electrode active material is preferably 0.5 to 2.6 mm ³ / (g · nm) from the viewpoint of discharge capacity and charge / discharge cycle performance, and is 0.6 to 0.6. 2.0mm ³ / (g · nm) are more ^{preferred, 0.7~1.5mm 3 / (g · nm} ) is more preferably more.

The pore diameter at which the differential pore volume of the lithium excess type positive electrode active material shows the maximum value is preferably in the range of 20 to 150 nm, preferably in the range of 20 to 100 nm, from the viewpoint of discharge capacity and high rate discharge performance. Is more preferable.

The lower limit of the total pore volume of the lithium-excess type positive electrode active material, the discharge capacity, in view of high rate discharge performance, is preferably 0.02 cm ³ / g, and more to be 0.04 cm ³ / g It is preferably 0.06 cm ³ / g, and more preferably 0.06 cm ³ / g. Further, the upper limit of the total pore volume may be 0.5 cm ³ / g, 0.3 cm ³ / g, or 0.15 cm ³ / g.

The lithium excess type positive electrode active material can be synthesized by mixing and firing a compound containing a transition metal element and a lithium compound. The X-ray diffraction pattern of the powder after synthesis (before charging and discharging) using CuKα rays is 2θ = 18.6 ± 1 °, 36.8 ± 1 ° derived from the crystal system belonging to the space group R3-m. , And 44.0 ± 1 ° diffraction peaks, and at 2θ = 20.8 ± 1 °, superlattice peaks derived from the crystal system belonging to the space groups C2 / m, C2 / c or P3 ₁ 12. Is confirmed. The space group C2 / m, C2 / c or P3 ₁ 12 is a crystal structure model in which the atomic positions of the 3a, 3b, and 6c sites in the space group R3-m are subdivided. In addition, "R3-m" is originally described by adding a bar "-" on "3" of "R3m".

The lithium excess type positive electrode active material according to the present embodiment is typified by alkali metals such as Na and K, alkaline earth metals such as Mg and Ca, and 3d transition metals such as Fe, as long as its characteristics are not significantly impaired. It may contain small amounts of other metals such as transition metals.

An aluminum compound may be coated and / or solid-solved on the surface of the primary particles and / or secondary particles of the lithium excess positive electrode active material. The presence of the aluminum compound on the particle surface prevents direct contact with the non-aqueous electrolyte, suppresses deterioration such as structural changes due to charge / discharge, and improves charge / discharge cycle performance. ..

As the positive electrode active material, the lithium excess type positive electrode active material may be used alone, or two or more kinds of lithium excess type positive electrode active materials having different physical properties may be mixed. Further, as long as the effect of the present invention is not impaired, a positive electrode active material other than the lithium excess type positive electrode active material may be mixed and used for the purpose of improving low temperature characteristics, improving output characteristics and the like. In this case, the mixing ratio of the positive electrode active material other than the lithium excess type positive electrode active material in the positive electrode active material may be 20% by mass or less.

The average particle size of the lithium excess type positive electrode active material is preferably 0.1 μm or more, more preferably 1 μm or more, and more preferably 5 μm or more. Further, it is preferably 20 μm or less. By setting the average particle size of the positive electrode active material to the above lower limit or more, the production or handling of the positive electrode active material becomes easy. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electron conductivity of the positive electrode mixture layer is improved. Here, the "average particle size" is based on JIS-Z-8825 (2013), and is based on the particle size distribution measured by a laser diffraction / scattering method with respect to a diluted solution obtained by diluting the particles with a solvent. It means a value at which the volume-based integrated distribution calculated in accordance with Z-8819-2 (2001) is 50%.

The amorphous carbon used for the positive electrode according to the present embodiment is preferably carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black.

The lower limit of the amorphous carbon content in the positive electrode mixture layer is preferably 1% by mass, more preferably 2% by mass, based on the mass of the positive electrode mixture layer. The upper limit of the amorphous carbon content is preferably 7% by mass, more preferably 5% by mass, based on the mass of the positive electrode mixture layer. By setting the content of amorphous carbon in the above range, the charge / discharge cycle performance can be improved.

The graphite used for the positive electrode according to the present embodiment is a carbonaceous material having a peak with a half width of 0.6 ° or less at 2θ = 26.4 ± 1 ° in X-ray diffraction measurement using CuKα rays. ..
In X-ray diffraction measurement using CuKα ray, the fact that the half width of the peak at 2θ = 26.4 ± 1 ° is 0.6 ° or less means that graphene is regularly laminated in the c-axis direction and the crystallinity is high. Means that. Therefore, when a force is applied to compress an electrode containing graphite in addition to the lithium excess positive electrode active material and amorphous carbon with a roll press or a flat plate press, the layers of graphene are displaced to increase the electrode density. It is considered that it can be improved (see FIG. 3). The upper limit of the half width of the peak of 2θ = 26.4 ± 1 ° is more preferably 0.5 ° and even more preferably 0.4 °.

The lower limit of the average particle size of graphite used for the positive electrode is preferably 3 μm, more preferably 9 μm. The upper limit of the average particle size is preferably 16 μm, more preferably 13 μm. By setting the average particle size of graphite in the above range, it is possible to provide a positive electrode having excellent charge / discharge cycle performance. Here, the average particle size is based on JIS-Z-8825 (2013), and is based on the particle size distribution measured by a laser diffraction / scattering method with respect to a diluted solution obtained by diluting the particles with a solvent. It means a value at which the volume-based integrated distribution calculated in accordance with 8819-2 (2001) is 50%.

The lower limit of the BET specific surface area of the graphite used for the positive electrode is preferably from ^{3m 2 / g, 4m 2 /} g is more preferable. The upper limit of the BET specific surface area is preferably ^{12m 2 / g, 10m 2 /} g is more preferable. By setting the BET specific surface area of graphite in the above range, it is possible to provide a positive electrode having excellent charge / discharge cycle performance.

The shape and type of graphite used for the positive electrode are not particularly limited as shown in Examples described later. For example, spheroidal graphite may be used, bulk graphite may be used, scaly graphite may be used, or flaky graphite may be used. The morphology of spheroidal graphite and massive graphite and the morphology of scaly graphite and flaky graphite are significantly different in terms of aspect ratio. Generally, the aspect ratio of spheroidal graphite and bulk graphite is 1 or more and less than 10, and the aspect ratio of scaly graphite and flaky graphite is 10 or more and 25 or less. In the present embodiment, graphite having an aspect ratio of 10 or more and 25 or less is preferable.

In graphite having an aspect ratio of 10 or more and 25 or less, the upper limit of the thickness may be 2 μm, 1 μm, or 0.5 μm. The thickness of graphite can be obtained from, for example, a cross-sectional SEM image of a positive electrode containing graphite. The thickness of graphite refers to the maximum dimension of graphite particles in the direction orthogonal to the surface of the graphite particles when viewed from the direction in which the area of the graphite particles is the largest.

The lower limit of the graphite content in the positive electrode mixture layer is preferably 0.2% by mass with respect to the mass of the positive electrode mixture layer. By setting it to the above lower limit or more, the electrode density can be improved. The upper limit of the graphite content is preferably 2% by mass, more preferably 1% by mass, and even more preferably 0.5% by mass with respect to the mass of the positive electrode mixture layer. By setting it to the above upper limit or less, the possibility that the electrochemical characteristics are deteriorated can be reduced. Therefore, the content of graphite in the positive electrode mixture layer is preferably 0.2 to 2% by mass, more preferably 0.2 to 1% by mass, and 0.2 to 0% by mass with respect to the mass of the positive electrode mixture layer. 5% by mass is even more preferable. By setting the graphite content in the above range, it is possible to improve the electrode density and reduce the risk of deterioration of electrochemical characteristics.

"Graphite mass ratio (= graphite mass / (graphite mass + amorphous carbon mass)) x 100 (%)" representing the mass ratio of amorphous carbon contained in the positive electrode mixture layer to graphite As the lower limit, 4% is preferable, and 6% is more preferable. By setting it to the above lower limit or more, the electrode density of the positive electrode can be improved. The upper limit of the graphite mass ratio is preferably 40%, more preferably 25%, and even more preferably 10%. By setting it to the above upper limit or less, the possibility that the electrochemical characteristics are deteriorated can be reduced.

<X-ray diffraction measurement>
In the present specification, the X-ray diffraction measurement is performed using an X-ray diffraction apparatus manufactured by Rigaku Corporation (product number: RINT-TTR3) under the following conditions. The radiation source is CuKα, and the X-ray output is 50 kV, 300 mA. The scan mode is CONTINUOUS, the step width is 0.02 deg, the scan speed is 4.0 deg / min, the incident slit is 1/3 deg, the longitudinal limiting slit is 10 mm, the light receiving slit 1 is 1/3 deg, and the light receiving slit 2 is 0.3 mm. To do.

<Peak differential pore volume measurement>
In the present specification, the peak differential pore volume measurement is measured by the following method.
1.00 g of the powder of the sample to be measured is placed in a sample tube for measurement and vacuum dried at 120 ° C. for 6 hours and 180 ° C. for 6 hours to sufficiently remove the water content in the measurement sample. Next, the isotherms on the adsorption side and the desorption side are measured within a range of 0 to 1 in relative pressure P / P0 (P0 = about 770 mmHg) by a nitrogen gas adsorption method using liquid nitrogen. Then, the cumulative pore volume curve is obtained by the BJH method using the isothermal line on the desorption side. From this curve, the value of total pore volume (cm ³ / g) is obtained. Next, by linearly differentiating the cumulative pore volume curve, the horizontal axis is the pore diameter (nm) and the vertical axis is the differential pore volume (mm ³ / (g · nm)). Obtain a hole volume curve. In the present specification, the “peak differential pore volume” refers to the value on the vertical axis corresponding to the point where the differential pore volume curve shows the maximum value. A large "peak differential pore volume" means that the number of pores having a certain pore diameter is large. Further, in the present specification, the "pore diameter showing the maximum value of the differential pore volume" means the value on the horizontal axis corresponding to the point where the differential pore volume curve shows the maximum value.

<Measurement of average particle size>
A Microtrac (model number: MT3000) manufactured by Nikkiso Co., Ltd. is used as the measuring device. The measuring device comprises an optical table, a sample supply unit, and a computer equipped with control software, and a wet cell equipped with a laser light transmitting window is installed in the optical table. The measurement principle is a method in which a wet cell in which a dispersion liquid in which a measurement target sample is dispersed in a dispersion solvent circulates is irradiated with laser light, and the scattered light distribution from the measurement sample is converted into a particle size distribution. The dispersion is stored in the sample supply section and circulated and supplied to the wet cell by a pump. Ethanol is used as the dispersion solvent. Microtrac DHS for Win98 (MT3000) is used as the measurement control software. For the "substance information" to be set and input to the measuring device, "Reflection" is selected as the "transparency". Further, 1.36 is set as the "refractive index" of the solvent. Prior to the measurement of the sample, a "Set Zero" operation is performed. The "Set Zero" operation is an operation for subtracting the influence of disturbance elements (glass, dirt on the glass wall surface, glass unevenness, etc.) other than the scattered light from the particles on the subsequent measurement, and is an operation for subtracting the influence of the dispersion solvent on the sample supply part. A background measurement is performed in a state where only a certain ethanol is put in and only ethanol, which is a dispersion solvent, is circulated in the wet cell, and the background data is stored in the computer. Subsequently, the "Sample LD (Sample Loading)" operation is performed. The Sample LD operation is an operation for optimizing the sample concentration in the dispersion liquid that is circulated and supplied to the wet cell at the time of measurement, and manually reaches the optimum amount of the sample to be measured in the sample supply unit according to the instruction of the measurement control software. It is an operation to put in. Then, the measurement operation is performed by pressing the "measurement" button. The above measurement operation is repeated twice, and the measurement result is output from the control computer as the average value. The measurement results are obtained as the particle size distribution and the respective values of D10, D50 and D90 (D10, D50 and D90 are particle sizes in which the cumulative volumes in the particle size distribution of the secondary particles are 10%, 50% and 90%, respectively). Will be done. The division width of the particle size distribution is set as 0.01% for the frequency on the vertical axis and 0.0376 for the particle size with the common logarithm on the horizontal axis. The obtained value of D50 is used as the average particle size.

<Measurement of BET specific surface area>
The amount of nitrogen adsorbed on the sample (m ² ) is determined by a one-point method using a specific surface area measuring device (trade name: MONOSORB) manufactured by Yuasa Ionics. The value obtained by dividing the obtained adsorption amount by the mass (g) of the sample is defined as the BET specific surface area (m ² / g). In the measurement, gas adsorption is performed by cooling with liquid nitrogen. In addition, preheating is performed at 120 ° C. for 15 minutes before cooling. The input amount of the measurement sample is 0.2 g ± 0.01 g for graphite.

<Adjustment of measurement sample>
Samples to be used for each measurement of the positive electrode active material according to the present embodiment and the active material contained in the positive electrode included in the non-aqueous electrolyte power storage element according to the present embodiment are prepared according to the following procedures and conditions.
If the sample to be measured is a powder sample before the positive electrode is prepared, it is used as it is for measurement.
When a sample is collected from the positive electrode taken out by disassembling the battery, the amount of electricity equal to the nominal capacity (Ah) of the battery is one tenth of the current energized in one hour before disassembling the battery. With the current value (A), constant current discharge is performed up to the battery voltage which is the lower limit of the specified voltage, and the state is set to the discharged state. As a result of disassembly, if the battery uses a metallic lithium electrode as the negative electrode, the positive electrode mixture collected from the positive electrode is the measurement target without performing the additional work described below. If the battery does not use a metallic lithium electrode as the negative electrode, in order to accurately control the positive electrode potential, a battery with the positive electrode taken out by disassembling the battery as the working electrode and the metallic lithium electrode as the counter electrode is assembled, and the positive electrode mixture 1 g. With a current value of 10 mA per unit, constant current discharge is performed until the voltage reaches 2.0 V, adjusted to the discharged state, and then disassembled again. The positive electrode taken out is thoroughly washed with dimethyl carbonate to thoroughly wash the adhered non-aqueous electrolyte, dried at room temperature for 24 hours, and then the positive electrode mixture is collected from the positive electrode. The work from disassembly to re-disassembly of the battery, and the cleaning and drying work of the positive electrode plate are performed in an argon atmosphere having a dew point of −60 ° C. or lower.
For the sample to be used for X-ray diffraction measurement, the above mixture is crushed in an agate mortar and then used for measurement.
For the sample to be used for the peak differential pore volume measurement, the conductive agent and the binder are removed by firing the above mixture at 600 ° C. for 2 hours in a small electric furnace, and the obtained powder is used for the measurement. ..

<Structure of non-aqueous electrolyte power storage element>
The non-aqueous electrolyte power storage element (hereinafter, also simply referred to as “storage element”) according to the embodiment of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. As an example of the non-aqueous electrolyte power storage element, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as “secondary battery”) will be described.

(Positive electrode)
The positive electrode has a positive electrode base material and a positive electrode mixture layer arranged directly on the positive electrode base material or via an intermediate layer.

The positive electrode base material has conductivity. As the material of the positive electrode base material, metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof are used. Among these, aluminum or an aluminum alloy is preferable from the viewpoint of potential resistance, high conductivity, and cost. Examples of the positive electrode base material include foil and a vapor-deposited film, and foil is preferable from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferable as the positive electrode base material. Examples of aluminum or aluminum alloy include A1085 and A3003 specified in JIS-H-4000 (2014).

As the lower limit of the average thickness of the positive electrode base material, 5 μm is preferable, and 10 μm is more preferable. The upper limit of the average thickness of the positive electrode base material is preferably 30 μm, more preferably 20 μm. By setting the average thickness of the positive electrode base material to the above lower limit or more, the strength of the positive electrode base material can be increased. By setting the average thickness of the positive electrode base material to be equal to or less than the above upper limit, the energy density per volume of the secondary battery can be increased. "Average thickness" means the average value of the thickness measured at any ten points. The same definition applies when the "average thickness" is used for other members and the like.

The intermediate layer is a layer arranged between the positive electrode base material and the positive electrode mixture layer. The intermediate layer contains conductive particles such as carbon particles to reduce the contact resistance between the positive electrode base material and the positive electrode mixture layer. The composition of the intermediate layer is not particularly limited, and includes, for example, a resin binder and conductive particles.

The positive electrode mixture layer contains a positive electrode active material. The positive electrode mixture layer contains optional components such as a conductive agent, a binder (binder), a thickener, and a filler, if necessary.

A crusher, a classifier, or the like is used to obtain the powder in a predetermined shape. Examples of the crushing method include a method using a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow type jet mill, a sieve, or the like. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. As a classification method, a sieve, a wind power classifier, or the like is used as needed for both dry and wet types.

The lower limit of the content of the positive electrode active material in the positive electrode mixture layer is preferably 90% by mass, more preferably 93% by mass, still more preferably 95% by mass, based on the mass of the positive electrode mixture layer. By setting the content of the positive electrode active material to the above lower limit or more, the discharge capacity can be increased. The upper limit of the content of the positive electrode active material is preferably 99% by mass, more preferably 97% by mass, based on the mass of the positive electrode mixture layer. By setting the content of the positive electrode active material particles to the above upper limit or less, the production of the positive electrode becomes easy.

Examples of the binder (binding agent) include fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, and polyimide; ethylene-propylene-diene rubber (EPDM). , Elastomers such as sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber; and thermoplastic polymers.

The lower limit of the content of the binder in the positive electrode mixture layer is preferably 1% by mass, more preferably 3% by mass, based on the mass of the positive electrode mixture layer. The upper limit of the content of the binder is preferably 7% by mass, more preferably 5% by mass, based on the mass of the positive electrode mixture layer. By setting the content of the binder within the above range, the active material can be stably retained.

Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, this functional group may be inactivated by methylation or the like in advance.

The filler is not particularly limited. Examples of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, glass, aluminosilicate and the like.

The positive electrode mixture layer is a typical non-metal element such as B, N, P, F, Cl, Br, I, a typical metal element such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sc. , Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, W and other transition metal elements as components other than positive electrode active materials, conductive agents, binders, thickeners and fillers. It may be contained.

(Negative electrode)
The negative electrode has a negative electrode base material and a negative electrode mixture layer arranged directly on the negative electrode base material or via an intermediate layer. The configuration of the intermediate layer is not particularly limited, and for example, it can be selected from the configurations exemplified by the positive electrode.

The negative electrode base material has conductivity. As the material of the negative electrode base material, copper, nickel, stainless steel, nickel-plated steel metal or an alloy thereof is used. Among these, copper or a copper alloy is preferable. Examples of the negative electrode base material include foil and a vapor-deposited film, and foil is preferable from the viewpoint of cost. Therefore, a copper foil or a copper alloy foil is preferable as the negative electrode base material. Examples of the copper foil include rolled copper foil, electrolytic copper foil and the like.

The lower limit of the average thickness of the negative electrode base material is preferably 3 μm, more preferably 5 μm. The upper limit of the average thickness of the negative electrode base material is preferably 30 μm, more preferably 20 μm. By setting the average thickness of the negative electrode base material to be equal to or higher than the above lower limit, the strength of the negative electrode base material can be increased. By setting the average thickness of the negative electrode base material to be equal to or less than the above upper limit, the energy density per volume of the secondary battery can be increased.

The negative electrode mixture layer contains a negative electrode active material. The negative electrode mixture layer contains optional components such as a conductive agent, a binder (binder), a thickener, and a filler, if necessary. Optional components such as a conductive agent, a binder, a thickener, and a filler can be selected from the materials exemplified by the positive electrode.

The negative electrode mixture layer is a typical non-metal element such as B, N, P, F, Cl, Br, I, a typical metal element such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sc. , Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W and other transition metal elements as negative electrode active materials, conductive agents, binders, thickeners, fillers. It may be contained as a component other than.

The negative electrode active material can be appropriately selected from known negative electrode active materials. As the negative electrode active material for a lithium ion secondary battery, a material capable of occluding and releasing lithium ions is usually used. Examples of the negative electrode active material include metal Li; metal or semi-metal such as Si and Sn; metal oxide or semi-metal oxide such as Si oxide, Ti oxide and Sn oxide; Li ₄ Ti ₅ O ₁₂ ; Titanium-containing oxides such as LiTIO _{2 and} TiNb ₂ O ₇ ; polyphosphate compounds; silicon carbide; carbon materials such as graphite (graphite) and non-graphitizable carbon (graphitizable carbon or non-graphitizable carbon). Be done. Among these materials, graphite and non-graphitic carbon are preferable. In the negative electrode mixture layer, one of these materials may be used alone, or two or more of these materials may be mixed and used.

Graphite used for the negative electrode refers to a carbon material having an average lattice spacing (d ₀₀₂ ) of (002) planes determined by X-ray diffraction method of 0.33 nm or more and less than 0.34 nm before charging / discharging or in a discharged state. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferable from the viewpoint that a material having stable physical properties can be obtained.

“Non-graphitic carbon” refers to a carbon material having an average lattice spacing (d ₀₀₂ ) of (002) planes determined by X-ray diffraction before charging / discharging or in a discharged state of 0.34 nm or more and 0.42 nm or less. .. Examples of non-graphitizable carbon include non-graphitizable carbon and easily graphitizable carbon. Examples of the non-graphitic carbon include a resin-derived material, a petroleum pitch or a petroleum pitch-derived material, a petroleum coke or a petroleum coke-derived material, a plant-derived material, an alcohol-derived material and the like.

The “non-graphitizable carbon” refers to a carbon material having d ₀₀₂ of 0.36 nm or more and 0.42 nm or less.

The “graphitizable carbon” refers to a carbon material in which d ₀₀₂ is 0.34 nm or more and less than 0.36 nm.

The average particle size of the negative electrode active material can be, for example, 1 μm or more and 100 μm or less. By setting the average particle size of the negative electrode active material to the above lower limit or more, the production or handling of the negative electrode active material becomes easy. By setting the average particle size of the negative electrode active material to the above upper limit or less, the electron conductivity of the mixture layer is improved. A crusher, a classifier, or the like is used to obtain the powder in a predetermined shape. The pulverization method and the powder grade method can be selected from, for example, the methods exemplified for the positive electrode.

The lower limit of the content of the negative electrode active material in the negative electrode mixture layer is preferably 60% by mass, more preferably 80% by mass, and even more preferably 90% by mass. By setting the content of the negative electrode active material to the above lower limit or more, the electric capacity of the secondary battery can be increased. The upper limit of the content of the negative electrode active material is preferably 99% by mass, more preferably 98% by mass. By setting the content of the negative electrode active material particles to the above upper limit or less, the production of the negative electrode becomes easy.

(Separator)
The separator can be appropriately selected from known separators. As the separator, for example, a separator composed of only a base material layer, a separator having a heat-resistant layer containing heat-resistant particles and a binder formed on one surface or both surfaces of the base material layer can be used. Examples of the material of the base material layer of the separator include woven fabrics, non-woven fabrics, and porous resin films. Among these materials, a porous resin film is preferable from the viewpoint of strength, and a non-woven fabric is preferable from the viewpoint of liquid retention of a non-aqueous electrolyte. As the material of the base material layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of shutdown function, and polyimide and aramid are preferable from the viewpoint of oxidative decomposition resistance. A composite material of these resins may be used as the base material layer of the separator.

The heat-resistant particles contained in the heat-resistant layer preferably have a weight loss of 5% or less at 500 ° C. in the atmosphere, and more preferably 5% or less in weight loss at 800 ° C. in the air. Inorganic compounds can be mentioned as materials whose weight loss is less than or equal to a predetermined value. Examples of the inorganic compound include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, zirconium oxide, and aluminum oxide-silicon oxide composite oxide; nitrides such as aluminum nitride and silicon nitride; fluoride. Slowly soluble ionic crystals such as calcium, barium fluoride, barium sulfate; covalent crystals such as silicon and diamond; talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mulite, spinel, olivine, sericite, bentonite, mica Examples thereof include substances derived from mineral resources such as, or artificial products thereof. As the inorganic compound, a simple substance or a complex of these substances may be used alone, or two or more kinds thereof may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminum oxide-silicon oxide composite oxide is preferable.

The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and preferably 20% by volume or more from the viewpoint of discharge performance. Here, the "vacancy ratio" is a volume-based value, and means a value measured by a mercury porosimeter.

As the separator, a polymer gel composed of a polymer and a non-aqueous electrolyte may be used. Examples of the polymer include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethylmethacrylate, polyvinylacetate, polyvinylpyrrolidone, polyvinylidene fluoride and the like. The use of polymer gel has the effect of suppressing liquid leakage. As the separator, a polymer gel may be used in combination with the above-mentioned porous resin film or non-woven fabric.

(Non-aqueous electrolyte)
The non-aqueous electrolyte can be appropriately selected from known non-aqueous electrolytes. A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of the non-aqueous solvent include cyclic carbonate, chain carbonate, carboxylic acid ester, phosphoric acid ester, sulfonic acid ester, ether, amide, nitrile and the like. As the non-aqueous solvent, those in which some of the hydrogen atoms contained in these compounds are replaced with halogen may be used.

As the cyclic carbonate, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate. (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate and the like can be mentioned. Of these, EC is preferable.

Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, and bis (trifluoroethyl) carbonate. Of these, EMC is preferable.

As the non-aqueous solvent, it is preferable to use cyclic carbonate or chain carbonate, and it is more preferable to use cyclic carbonate and chain carbonate in combination. By using the cyclic carbonate, the dissociation of the electrolyte salt can be promoted and the ionic conductivity of the non-aqueous electrolyte solution can be improved. By using the chain carbonate, the viscosity of the non-aqueous electrolyte can be kept low. When the cyclic carbonate and the chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate: chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt and the like. Of these, lithium salts are preferred.

Lithium salts include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO _2). C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ C ₂ F ₅ ) _{3 and} other halogenated hydrocarbon groups Examples thereof include lithium salts having. Among these, an inorganic lithium salt is preferable, and LiPF ₆ is more preferable.

The lower limit of the content of the electrolyte salt in the non-aqueous electrolytic solution is preferably 0.1 mol / L, more preferably 0.3 mol / L, further preferably 0.5 mol / L, and particularly preferably 0.7 mol / L. As the upper limit of the content of the electrolyte salt, for example, 2.5 mol / L is preferable, 2 mol / L is more preferable, and 1.5 mol / L is further preferable.

The non-aqueous electrolyte solution may contain additives. Examples of the additive include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); lithium bis (oxalate) borate (LiBOB), lithium difluorooxalate borate (LiFOB), lithium bis (oxalate). ) Salts having a oxalic acid group such as difluorophosphate (LiFOP); imide salts such as lithium bis (fluorosulfonyl) imide (LiFSI); partial hydrides of biphenyl, alkylbiphenyl, terphenyl, terphenyl, cyclohexylbenzene, t Aromatic compounds such as −butylbenzene, t-amylbenzene, diphenyl ether and dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene and p-cyclohexylfluorobenzene; 2,4-difluoro Halogenated anisole compounds such as anisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, succinic anhydride, glutaric anhydride, maleine anhydride Acid, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sulton, propensulton, butane sulton, methyl methanesulfonate, busulphan, methyl toluenesulfonate, sulfuric acid Dimethyl, ethylene sulfate, sulfolane, dimethylsulfone, diethylsulfone, dimethylsulfoxide, diethylsulfoxide, tetramethylenesulfoxide, diphenylsulfide, 4,4'-bis (2,2-dioxo-1,3,2-dioxathiolane, 4-methyl) Sulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisol, diphenyldisulfide, dipyridinium disulfide, perfluorooctane, tritrimethylsilyl borate, tritrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, monofluorophosphorus Examples thereof include lithium acid and lithium difluorophosphate. These additives may be used alone or in combination of two or more.

The lower limit of the content ratio of these additives with respect to the entire non-aqueous electrolyte solution is preferably 0.01% by mass, more preferably 0.1% by mass, and even more preferably 0.2% by mass. As the upper limit of the content ratio of the additive, 10% by mass is preferable, 7% by mass is more preferable, 5% by mass is more preferable, and 3% by mass is further preferable. By setting the content ratio of the additive in the above range, it is possible to improve the capacity maintenance performance or charge / discharge cycle performance after high temperature storage, and further improve the safety.

As the non-aqueous electrolyte, a solid electrolyte may be used, or a non-aqueous electrolyte solution and a solid electrolyte may be used in combination.

The solid electrolyte can be selected from any material having ionic conductivity such as lithium, sodium and calcium and being solid at room temperature (for example, 15 ° C. to 25 ° C.). Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, polymer solid electrolytes and the like.

Examples of the sulfide solid electrolyte include Li ₂ SP ₂ S ₅ series in the case of a lithium ion secondary battery. Examples of the sulfide solid electrolyte include Li ₂ SP ₂ S ₅ , Li I-Li ₂ SP ₂ S ₅ , Li ₁₀ Ge-P ₂ S ₁₂ , and the like.

The shape of the power storage element of the present embodiment is not particularly limited, and examples thereof include a cylindrical battery, a laminated film type battery, a square battery, a flat type battery, a coin type battery, and a button type battery.
FIG. 1 shows an example of a square non-aqueous electrolyte secondary battery as an embodiment of the power storage element of the present invention. The positive electrode wound around the separator and the electrode body 2 having the negative electrode are housed in the square case 3. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4'. The negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5'.

<Configuration of non-aqueous electrolyte power storage device>
The power storage element of the present embodiment stores a plurality of power storage elements in an electric vehicle (EV), a power source for an automobile such as a plug-in hybrid vehicle (PHEV), a power source for an electronic device such as a personal computer or a communication terminal, or a power source for power storage. It can be mounted as a power storage unit (battery module) formed by assembling the elements 1. In this case, the technique of the present invention may be applied to at least one power storage element included in the power storage device.
FIG. 2 shows an example of a power storage device 30 in which a power storage unit 20 in which two or more electrically connected power storage elements 1 are assembled is further assembled. The power storage device 30 may include a bus bar (not shown) that electrically connects two or more power storage elements 1 and a bus bar (not shown) that electrically connects two or more power storage units 20. The power storage unit 20 or the power storage device 30 may include a condition monitoring device (not shown) that monitors the state of one or more power storage elements.

<Manufacturing method of non-aqueous electrolyte power storage element>
The method for manufacturing the power storage element of the present embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, a step of preparing an electrode body, a step of preparing a non-aqueous electrolyte, and a step of accommodating the electrode body and the non-aqueous electrolyte in a container. The step of preparing the electrode body includes a step of preparing a positive electrode body and a negative electrode body, and a step of forming the electrode body by laminating or winding the positive electrode body and the negative electrode body via a separator.

The step of accommodating the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when a non-aqueous electrolyte solution is used as the non-aqueous electrolyte solution, the non-aqueous electrolyte solution may be injected from the injection port formed in the container, and then the injection port may be sealed.

<Other Embodiments>
The power storage element of the present invention is not limited to the above embodiment, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment or a well-known technique. In addition, some of the configurations of certain embodiments can be deleted. Further, a well-known technique can be added to the configuration of a certain embodiment.

In the above embodiment, the case where the power storage element is used as a non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) capable of charging and discharging has been described, but the type, shape, size, capacity, etc. of the power storage element are arbitrary. .. The present invention can also be applied to capacitors such as various secondary batteries, primary batteries, electric double layer capacitors and lithium ion capacitors.

Hereinafter, the present invention will be described in more detail with reference to Examples. The present invention is not limited to the following examples.

[Preparation of lithium excess positive electrode active material (LR1)]
<Synthesis of lithium excess positive electrode active material>
17.7 g of nickel sulfate hexahydrate and 32.5 g of manganese sulfate pentahydrate were weighed, and the total amount of these was dissolved in 200 mL of ion-exchanged water, and the molar ratio of Ni: Mn was 33.3: 66.7. A 1.0 mol / L sulfate aqueous solution was prepared. On the other hand, CO ₂ was dissolved in the ion-exchanged water by pouring 750 mL of ion-exchanged water into a ₂ L reaction vessel and bubbling CO ₂ gas for 30 minutes. The temperature of the reaction vessel is set to 50 ° C. (± 2 ° C.), and the above sulfate aqueous solution is stirred at a speed of 2 mL / min while stirring the inside of the reaction vessel at a rotation speed of 700 rpm using a paddle blade equipped with a stirring motor. Dropped. Here, the pH in the reaction vessel is always maintained at 7.9 (± 0.05) by appropriately dropping an aqueous solution containing 1.0 mol / L sodium carbonate from the start to the end of the dropping. Controlled to. After completion of the dropping, stirring in the reaction vessel was continued for another 5 hours. After the stirring was stopped, the mixture was allowed to stand for 12 hours or more.
Next, the particles of coprecipitated carbonate generated in the reaction vessel are separated using a suction filtration device, and the sodium ions adhering to the particles are washed and removed using ion-exchanged water, and an electric furnace is used. Then, it was dried at 80 ° C. for 20 hours under normal pressure in an air atmosphere. Then, in order to make the particle size uniform, it was crushed in an agate mortar for several minutes. In this way, a coprecipitated carbonate precursor was prepared.

To 2.8 g of the coprecipitated carbonate precursor, 1.2 g of lithium carbonate was added and mixed well using an agate mortar, and the mixture had a molar ratio of Li: Me (total of Ni and Mn) of 1.33. A powder was prepared. It was molded at a pressure of 40 MPa using a pellet molding machine to obtain pellets having a diameter of 25 mm. The amount of the mixed powder used for pellet molding was determined by converting so that the assumed mass of the final product was 2.5 g. One of the pellets is placed on the lid of an alumina crucible with a total length of about 50 mm, installed in a box-type electric furnace (model number: AMF20), and takes 10 hours from room temperature to 890 ° C in an air atmosphere under normal pressure. The temperature was raised, and after the temperature was raised, it was fired for 9 hours at the temperature. The internal dimensions of the box-type electric furnace are 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was switched off, and the lid of the alumina crucible was left in the furnace to allow it to cool naturally. As a result, the temperature of the furnace drops to about 200 ° C. after 5 hours, but the subsequent temperature decrease rate is rather slow. After a day and night, after confirming that the temperature of the furnace was 100 ° C. or lower, the pellets were taken out and crushed in an agate mortar for several minutes in order to make the particle size uniform. In this way, a lithium excess type positive electrode active material Li _1.14 Ni _0.29 Mn _0.57 O ₂ (Li / Me = 1.33) was prepared.

<Aluminum treatment of lithium excess positive electrode active material>
Aluminum sulfate hydrate and ion-exchanged water were mixed in a 300 mL Erlenmeyer flask to prepare an aqueous aluminum sulfate solution having an aluminum sulfate content of 0.5 mol / L. 5.0 g of the above-mentioned lithium excess type positive electrode active material was added to the place where the above-mentioned aluminum sulfate aqueous solution was stirred at 25 ° C. and 400 rpm using a stirrer. The lithium-rich positive electrode active material was charged, and then suction filtration was performed 30 seconds later to recover the lithium-rich positive electrode active material on the filter paper.
This lithium-rich positive electrode active material was dried in air at normal pressure at 80 ° C. for 20 hours using a dryer to obtain an aluminum-treated lithium-rich positive electrode active material.

<Heat treatment of aluminum-treated lithium excess positive electrode active material>
The above aluminum-treated lithium-rich positive electrode active material is placed on the lid of an alumina crucible and installed in a box-type electric furnace (model number: AMF20). In air, the temperature rise rate is 5 ° C./min and the heat treatment temperature is high. By heat-treating under the conditions of 400 ° C. and a holding time of 4 hours, an aluminum-coated lithium-rich positive electrode active material (hereinafter, referred to as “LR1”) according to Example 1-1 was obtained. Li / Me of LR1 was 1.33, and the peak differential pore volume measured under the above conditions was 0.98 mm ³ / (g · nm).

[Preparation of positive electrode active material (LR2)]
Lithium excess type positive electrode according to Example 1-5 in the same manner as in Example 1-1, except that the firing temperature of the pellet obtained by mixing the coprecipitated carbonate precursor and lithium carbonate was changed to 930 ° C. The active material Li _1.14 Ni _0.29 Mn _0.57 O ₂ (hereinafter referred to as “LR2”) was prepared. Li / Me of LR2 was 1.33, and the peak differential pore volume measured under the above conditions was 0.72 mm ³ / (g · nm).

[Preparation of positive electrode active material (LR3)]
The molar ratio of Ni: Co: Mn of the co-precipitated carbonate precursor was changed to 19.5: 12.3: 68.2, and the precursor was used to make Li: Me (total of Ni, Co and Mn). Example 1 is the same as in Example 1-1, except that a mixed powder having a molar ratio of 1.38 is prepared and the firing temperature of pellets formed from the powder is changed to 900 ° C. Lithium excess type positive electrode active material Li _1.17 Ni _0.16 Co _0.1 Mn _0.57 O ₂ (hereinafter referred to as “LR3”) according to −6 was prepared. In addition, cobalt sulfate heptahydrate was used as a Co source. Li / Me of LR3 was 1.38, and the peak differential pore volume measured under the above conditions was 2.53 mm ³ / (g · nm).

[Preparation of positive electrode according to Example 1-1]
LR1 was used as the positive electrode active material, acetylene black (AB) was used as the amorphous carbon, flaky graphite was used as the graphite, and polyvinylidene fluoride (PVdF) was used as the binder. Positive electrode active material: Amorphous carbon: Graphite: Binder = 95.5: 2.5: 0.5: 1.5 (in terms of solid matter), N-methylpyrrolidone (NMP) as a dispersion medium A positive electrode paste was prepared. This positive electrode paste was applied to one side of an aluminum foil which is a positive electrode base material. After that, it was dried at 100 ° C. for 1 hour to remove NMP in the electrode plate.

[Preparation of positive electrode according to Examples 1-2 to 1-4]
Examples 1-2 to 1-4 are the same as in Example 1-1, except that the graphite is changed to scaly graphite, spheroidal graphite, and massive graphite instead of flaky graphite. Such positive electrodes were prepared respectively.

[Preparation of positive electrode according to Comparative Example 1-1]
Same as in Example 1-1 except that the ratio of positive electrode active material: amorphous carbon: binder = 95.5: 3.0: 1.5 (in terms of solid matter) was used without using graphite. A positive electrode according to Comparative Example 1-1 was prepared.

[Preparation of positive electrode according to Example 1-5 and Comparative Example 1-2]
The positive electrodes according to Examples 1-5 and 1-2 were prepared in the same manner as in Example 1-1 and Comparative Example 1-1, except that the positive electrode active material was LR2. did.

[Preparation of positive electrode according to Example 1-6 and Comparative Example 1-3]
The positive electrodes according to Examples 1-6 and 1-3 were produced in the same manner as in Example 1-1 and Comparative Example 1-1, except that the positive electrode active material was LR3. ..

[Preparation of positive electrode according to Reference Example 1-1 to Reference Example 1-4]
The positive electrode active material is a commercially available positive electrode active material LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (hereinafter referred to as “NCM523”) shown in Table 1, or LiNi _0.33 Co _0.33 Mn _0.33 O. _The positive electrodes according to Reference Example 1-1 and Reference Example 1-3 were produced in the same manner as in Example 1-1, except that ₂ (hereinafter referred to as “NCM111”) was used. Further, the positive electrodes according to Reference Example 1-2 and Reference Example 1-4 were produced in the same manner as in Comparative Example 1-1, respectively. In addition, the peak differential pore volume of these positive electrode active materials was also measured under the above conditions.

FIG. 4 shows SEM images of flaky graphite, scaly graphite, spheroidal graphite, and lump graphite. Further, for these graphites, the average particle size and the BET specific surface area were determined under the above conditions.

<Press test>
A press test was performed on the positive electrodes according to Examples 1-1 to 1-6, Comparative Examples 1-1 to 1-3, and Reference Examples 1-1 to 1-4.
After punching the electrode plate before pressing to 2 × 2 cm ² , roll pressing was performed at room temperature. Specifically, the plates were passed through the press multiple times until there was no change in thickness. In addition, the "electrode density (g / cm ³ )" of the mixture at that time was determined. Here, the electrode density is defined as "(mass of the positive electrode test piece used for the test)-(mass of the positive electrode base material)" (unit: g) and "volume of the mixture (2 x 2 x (positive electrode base material)". The thickness of the positive electrode to be excluded)) ”(unit: cm ³ ).

<X-ray diffraction measurement>
The positive electrodes according to Example 1-1 and Comparative Example 1-1 were pressed, and X-ray diffraction measurement using a Cu tube was performed under the above conditions. The result is shown in FIG. In Example 1-1, a peak derived from graphite was observed near 26.4 °. The half width of this peak was 0.4 ° or less. Further, as a result of X-ray diffraction measurement of flaky graphite, scaly graphite, spheroidal graphite, and massive graphite powder before being used for the electrodes according to Examples 1-1 to 1-4, all of them were 26.4 °. The half width of the peak in the vicinity was 0.4 ° or less.

Physical properties of the positive electrode active material used for the positive electrodes according to Examples 1-1 to 1-6, Comparative Examples 1-1 to 1-3, and Reference Examples 1-1 to 1-4, physical properties of graphite, and a positive electrode mixture. The composition ratio of the above and the electrode density of the obtained positive electrode are summarized in Tables 1 to 3.

Comparing Comparative Example 1-1 and Examples 1-1 to 1-4, by using 0.5% by mass of graphite instead of reducing AB, which is amorphous carbon, by 0.5% by mass, graphite It was found that the electrode density was improved regardless of the shape and physical properties. Above all, the spheroidal graphite used in Examples 1-3 has an effect of improving the electrode density even though the average particle size is as large as about 12 μm. This suggests that the factor for improving the electrode density by using graphite is other than the shape of graphite.

That is, all of the graphite powders used for the positive electrodes of Examples 1-1 to 1-4 have a half width of 0.4 ° or less at the peak around 26.4 ° at the X-ray diffraction peak, and the crystallinity of graphite. Is high. Therefore, when the electrodes are pressed, slippage occurs between the graphene layers of graphite, and it is considered that the effect of improving the electrode density is obtained. Among the graphites, when flaky graphite was used, the electrode density was most improved. It is considered that this is because the flaky graphite was deformed when the press pressure was applied while the flaky graphite was in the gaps between the positive electrode active material particles.

Comparing Example 1-5 and Comparative Example 1-2, or Example 1-6 and Comparative Example 1-3, LR2 and LR3 having different peak differential pore volumes and active material compositions are used as positive electrode active materials. Even when LR1 was used, the electrode density was improved as in the case of using LR1.

From Reference Examples 1-1 to 1-4, when NCM523 and NCM111 are used as the positive electrode active materials, the electrode density is 3.3 g / cm ³ or more, which is much higher than when the lithium excess positive electrode is used. It turns out that it is expensive. Moreover, the effect of improving the electrode density by using graphite was not observed.

[Evaluation of electrochemical characteristics]
The electrochemical characteristics of the positive electrode for which good results were obtained above were evaluated.
A positive electrode was prepared in the same manner as in Example 1-1, except that LR1 was used as the positive electrode active material and flaky graphite was used as the graphite species, and the contents of AB and graphite were as shown in Table 4. The positive electrode was pressed to obtain a positive electrode after pressing.

[Preparation of test cells according to Examples 2-1 to 2-4 and Comparative Example 2-1 (negative electrode: metallic lithium)]
Using the positive electrode after pressing, a test cell was prepared by the following procedure.
As a non-aqueous electrolyte (electrolyte solution), LiPF ₆ was added to a mixed solvent in which fluoroethylene carbonate and 2,2,2-trifluoroethylmethyl carbonate were mixed at a volume ratio of 3: 7 so that the concentration was 1 mol / L. A dissolved solution was used. As a separator, a fine pore film made of polypropylene whose surface was modified with polyacrylate was used. Metallic lithium was used for the negative electrode. For the exterior body, a metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal adhesive polypropylene film (50 μm) is used so that the positive electrode terminal and the open end of the negative electrode terminal are exposed to the outside. The electrodes were housed, and the fusion margin where the inner surfaces of the metal resin composite film faced each other was hermetically sealed except for the portion to be the liquid injection hole. After the electrolytic solution was injected, the liquid injection hole was sealed.

[Capacity confirmation test (negative electrode: metallic lithium)]
The capacity confirmation test of the above test cell was carried out in a constant temperature bath at 25 ° C. by the following procedure.
(1) Charging step Constant current constant voltage charging with a charging current of 0.1 C and a charging voltage of 4.7 V was performed. The charging termination condition was when the current was attenuated to 0.05C. After the charging was completed, a 10-minute rest was performed.
(2) Discharge process Constant current discharge was performed with a discharge end voltage of 2.0 V. After the end of the discharge, a 10-minute rest was performed.

The above (1) charging step and (2) discharging step were set as one charging / discharging step, and this charging / discharging step was repeated three times. The discharge current was 0.1 C for the first and second discharges, and the discharge current was 2 C for the third discharge.
The second discharge capacity (mAh) was divided by the mass of the positive electrode active material contained in the positive electrode and recorded as "0.1C discharge capacity (mAh / g, counter electrode lithium)". Similarly, the third discharge capacity (mAh) was divided by the mass of the positive electrode active material contained in the positive electrode and recorded as "2C discharge capacity (mAh / g, counter electrode lithium)".

[Preparation of test cells according to Examples 2-1 to 2-3 and Comparative Example 2-1 (negative electrode: graphite)]
Graphite was used as the negative electrode active material, carboxymethyl cellulose was used as the binder, and styrene-butadiene rubber was used as the thickener. Negative electrode active material: Binder: Thickener = 96.7: 2.1: 1.2 mass ratio (in terms of solid content) was contained to prepare a negative electrode paste using water as a dispersion medium. This negative electrode paste was applied to a copper foil as a negative electrode base material, dried, and pressed to prepare a graphite negative electrode.

The test using the graphite negative electrode according to Examples 2-1 to 2-3 and Comparative Example 2-1 was carried out in the same procedure as above except that the graphite negative electrode was used instead of metallic lithium as the negative electrode. A cell was prepared.

[Capacity confirmation test (negative electrode: graphite)]
The following capacity confirmation test was performed on the above test cell in a constant temperature bath at 25 ° C. according to the following procedure.
(1') Charging step Constant current constant voltage charging was performed with a charging current of 0.1 C and a charging voltage of 4.6 V. The charging termination condition was when the current was attenuated to 0.05C. After the charging was completed, a 10-minute rest was performed.
(2') Discharge process Constant current discharge was performed with a discharge current of 0.1 C and a discharge end voltage of 2.0 V. After the end of the discharge, a 10-minute rest was performed.

The (1') charging step and the (2') discharging step were set as one charging / discharging step, and this charging / discharging step was repeated twice. The second discharge capacity was recorded as the "initial discharge capacity".

[Charge / discharge cycle test (negative electrode: graphite)]
The test cell used for the capacity confirmation test was subjected to a charge / discharge cycle test according to the following procedure in a constant temperature bath at 25 ° C.
(1'') Charging step Constant current constant voltage charging with a charging current of 0.5 C and a charging voltage of 4.6 V was performed. The charging termination condition was when the current was attenuated to 0.1C. After the charging was completed, a 10-minute rest was performed.
(2 ″) Discharge step A constant current discharge with a discharge current of 1C and a discharge end voltage of 2.0V was performed. After the end of the discharge, a 10-minute rest was performed.

The (1 ″) charging step and the (2 ″) discharging step were set as one charging / discharging step, and this charging / discharging step was repeated 50 times.

[Capacity confirmation test after charge / discharge cycle test]
After the cell after the charge / discharge cycle test is subjected to constant current discharge with a discharge current of 0.1 C and a discharge end voltage of 2.0 V, it is charged once by the same procedure as the above-mentioned "capacity confirmation test (counterbode graphite)". Discharge was performed. The capacity at this time was recorded as "discharge capacity after 50 cycles". The percentage of the "discharge capacity after 50 cycles" with respect to the "initial discharge capacity" was calculated as the "maintenance rate after 50 cycles (%, counterpolar graphite)".

For each example and comparative example, "electrode density (g / cm ³ )", "0.1C discharge capacity (mAh / g, counter electrode lithium)", "2C discharge capacity (mAh / g, counter electrode lithium)", and " The maintenance rate after 50 cycles (%, counter electrode graphite) ”is shown in Table 4. Further, FIG. 7 shows the relationship between the graphite content of the positive electrode, the electrode density, and the 2C discharge capacity of the non-aqueous electrolyte power storage element. Here, the electrode density is indicated by “● (first axis)” and the 2C discharge capacity is indicated by “Δ (second axis)”.

As is clear from Table 4 and FIG. 7, in Examples 2-1 to 2-4 using the positive electrode containing 0.2 to 2% by mass of graphite, the electrode density was higher than that in Comparative Example 2-1. The improvement effect was confirmed. Then, as shown in Table 4, it was confirmed that in Examples 2-1 to 2-3, the excellent discharge performance and charge / discharge cycle performance equivalent to those of Comparative Example 2-1 were exhibited.

That is, by using amorphous carbon and graphite for the positive electrode containing the lithium excess type positive electrode active material, the electrode density can be improved without impairing the high discharge performance and the charge / discharge cycle performance.

According to the present invention, it is possible to provide a positive electrode having a high electrode density without impairing a high discharge capacity. Therefore, a non-aqueous electrolyte power storage element using this positive electrode can be used in addition to mobile devices such as mobile phones and personal computers, as well as electric vehicles. It is useful as an in-vehicle rechargeable battery for (EV), plug-in hybrid vehicles (PHV), and the like.

1 Non-aqueous electrolyte secondary battery 2 Electrode group 3 Battery container 4 Positive terminal 4'Positive lead 5 Negative terminal 5'Negative lead 20 Power storage unit 30 Power storage device

Claims (3)

A positive electrode for a non-aqueous electrolyte power storage element containing a lithium excess type positive electrode active material, amorphous carbon, and graphite. The positive electrode for a non-aqueous electrolyte power storage element according to claim 1, wherein the peak differential pore volume of the lithium excess type positive electrode active material is 0.5 mm ³ / (g · nm) or more. The non-aqueous electrolyte storage element provided with the positive electrode for the non-aqueous electrolyte storage element according to claim 1 or 2.